With development of wireless communication technologies, wireless communication apparatuses such as mobile phones, tablet computers, or the like, become more and more widely. Filters are used in the wireless communication devices for removing some unwanted frequency components from electrical signals to obtain frequency bands as desired. For example, a microstrip filter may be applied in a microphone device of the wireless communication apparatus for filtering noise components.
A typical microstrip filter is designed in a printed circuit board (PCB) in form of a buried capacitor or buried resistor. However, the above-mentioned microstrip filter has a high manufacturing cost and normally needs to occupy unduly large space in the wireless communication device, and moreover, a buried-resistor type microstrip filter is liable to suffer breakdown during an electro-static discharge (ESD) test of the PCB. In other words, the above-mentioned microstrip filter may be inapplicable to the microphone device of the wireless communication apparatus.
Therefore, it is desired to provide a microstrip filter and a microphone device using the microstrip filter which can overcome the aforesaid problems.